2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2013 Marco Costalba, Joona Kiiski, Tord Romstad
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
20 #include <algorithm> // For std::count
27 #include "ucioption.h"
29 using namespace Search;
31 ThreadPool Threads; // Global object
33 namespace { extern "C" {
35 // start_routine() is the C function which is called when a new thread
36 // is launched. It is a wrapper to the virtual function idle_loop().
38 long start_routine(Thread* th) { th->idle_loop(); return 0; }
43 // Thread c'tor starts a newly-created thread of execution that will call
44 // the the virtual function idle_loop(), going immediately to sleep.
46 Thread::Thread() /* : splitPoints() */ { // Value-initialization bug in MSVC
48 searching = exit = false;
49 maxPly = splitPointsSize = 0;
50 activeSplitPoint = NULL;
51 activePosition = NULL;
54 if (!thread_create(handle, start_routine, this))
56 std::cerr << "Failed to create thread number " << idx << std::endl;
62 // Thread d'tor waits for thread termination before to return
66 exit = true; // Search must be already finished
68 thread_join(handle); // Wait for thread termination
72 // TimerThread::idle_loop() is where the timer thread waits msec milliseconds
73 // and then calls check_time(). If msec is 0 thread sleeps until is woken up.
74 extern void check_time();
76 void TimerThread::idle_loop() {
83 sleepCondition.wait_for(mutex, msec ? msec : INT_MAX);
93 // MainThread::idle_loop() is where the main thread is parked waiting to be started
94 // when there is a new search. Main thread will launch all the slave threads.
96 void MainThread::idle_loop() {
104 while (!thinking && !exit)
106 Threads.sleepCondition.notify_one(); // Wake up UI thread if needed
107 sleepCondition.wait(mutex);
126 // Thread::notify_one() wakes up the thread when there is some search to do
128 void Thread::notify_one() {
131 sleepCondition.notify_one();
136 // Thread::wait_for() set the thread to sleep until condition 'b' turns true
138 void Thread::wait_for(volatile const bool& b) {
141 while (!b) sleepCondition.wait(mutex);
146 // Thread::cutoff_occurred() checks whether a beta cutoff has occurred in the
147 // current active split point, or in some ancestor of the split point.
149 bool Thread::cutoff_occurred() const {
151 for (SplitPoint* sp = activeSplitPoint; sp; sp = sp->parentSplitPoint)
159 // Thread::is_available_to() checks whether the thread is available to help the
160 // thread 'master' at a split point. An obvious requirement is that thread must
161 // be idle. With more than two threads, this is not sufficient: If the thread is
162 // the master of some split point, it is only available as a slave to the slaves
163 // which are busy searching the split point at the top of slaves split point
164 // stack (the "helpful master concept" in YBWC terminology).
166 bool Thread::is_available_to(Thread* master) const {
171 // Make a local copy to be sure doesn't become zero under our feet while
172 // testing next condition and so leading to an out of bound access.
173 int size = splitPointsSize;
175 // No split points means that the thread is available as a slave for any
176 // other thread otherwise apply the "helpful master" concept if possible.
177 return !size || (splitPoints[size - 1].slavesMask & (1ULL << master->idx));
181 // init() is called at startup to create and launch requested threads, that will
182 // go immediately to sleep due to 'sleepWhileIdle' set to true. We cannot use
183 // a c'tor becuase Threads is a static object and we need a fully initialized
184 // engine at this point due to allocation of Endgames in Thread c'tor.
186 void ThreadPool::init() {
188 sleepWhileIdle = true;
189 timer = new TimerThread();
190 push_back(new MainThread());
195 // exit() cleanly terminates the threads before the program exits
197 void ThreadPool::exit() {
199 delete timer; // As first because check_time() accesses threads data
201 for (iterator it = begin(); it != end(); ++it)
206 // read_uci_options() updates internal threads parameters from the corresponding
207 // UCI options and creates/destroys threads to match the requested number. Thread
208 // objects are dynamically allocated to avoid creating in advance all possible
209 // threads, with included pawns and material tables, if only few are used.
211 void ThreadPool::read_uci_options() {
213 maxThreadsPerSplitPoint = Options["Max Threads per Split Point"];
214 minimumSplitDepth = Options["Min Split Depth"] * ONE_PLY;
215 size_t requested = Options["Threads"];
217 assert(requested > 0);
219 while (size() < requested)
220 push_back(new Thread());
222 while (size() > requested)
230 // slave_available() tries to find an idle thread which is available as a slave
231 // for the thread 'master'.
233 Thread* ThreadPool::available_slave(Thread* master) const {
235 for (const_iterator it = begin(); it != end(); ++it)
236 if ((*it)->is_available_to(master))
243 // split() does the actual work of distributing the work at a node between
244 // several available threads. If it does not succeed in splitting the node
245 // (because no idle threads are available), the function immediately returns.
246 // If splitting is possible, a SplitPoint object is initialized with all the
247 // data that must be copied to the helper threads and then helper threads are
248 // told that they have been assigned work. This will cause them to instantly
249 // leave their idle loops and call search(). When all threads have returned from
250 // search() then split() returns.
253 void Thread::split(Position& pos, Stack* ss, Value alpha, Value beta, Value* bestValue,
254 Move* bestMove, Depth depth, Move threatMove, int moveCount,
255 MovePicker* movePicker, int nodeType) {
257 assert(pos.pos_is_ok());
258 assert(*bestValue <= alpha && alpha < beta && beta <= VALUE_INFINITE);
259 assert(*bestValue > -VALUE_INFINITE);
260 assert(depth >= Threads.minimumSplitDepth);
262 assert(splitPointsSize < MAX_SPLITPOINTS_PER_THREAD);
264 // Pick the next available split point from the split point stack
265 SplitPoint& sp = splitPoints[splitPointsSize];
267 sp.masterThread = this;
268 sp.parentSplitPoint = activeSplitPoint;
269 sp.slavesMask = 1ULL << idx;
271 sp.bestValue = *bestValue;
272 sp.bestMove = *bestMove;
273 sp.threatMove = threatMove;
276 sp.nodeType = nodeType;
277 sp.movePicker = movePicker;
278 sp.moveCount = moveCount;
284 // Try to allocate available threads and ask them to start searching setting
285 // 'searching' flag. This must be done under lock protection to avoid concurrent
286 // allocation of the same slave by another master.
287 Threads.mutex.lock();
291 activeSplitPoint = &sp;
292 activePosition = NULL;
294 size_t slavesCnt = 1; // This thread is always included
297 while ( (slave = Threads.available_slave(this)) != NULL
298 && ++slavesCnt <= Threads.maxThreadsPerSplitPoint && !Fake)
300 sp.slavesMask |= 1ULL << slave->idx;
301 slave->activeSplitPoint = &sp;
302 slave->searching = true; // Slave leaves idle_loop()
303 slave->notify_one(); // Could be sleeping
306 // Everything is set up. The master thread enters the idle loop, from which
307 // it will instantly launch a search, because its 'searching' flag is set.
308 // The thread will return from the idle loop when all slaves have finished
309 // their work at this split point.
310 if (slavesCnt > 1 || Fake)
313 Threads.mutex.unlock();
315 Thread::idle_loop(); // Force a call to base class idle_loop()
317 // In helpful master concept a master can help only a sub-tree of its split
318 // point, and because here is all finished is not possible master is booked.
320 assert(!activePosition);
322 // We have returned from the idle loop, which means that all threads are
323 // finished. Note that setting 'searching' and decreasing splitPointsSize is
324 // done under lock protection to avoid a race with Thread::is_available_to().
325 Threads.mutex.lock();
331 activeSplitPoint = sp.parentSplitPoint;
332 activePosition = &pos;
333 pos.set_nodes_searched(pos.nodes_searched() + sp.nodes);
334 *bestMove = sp.bestMove;
335 *bestValue = sp.bestValue;
338 Threads.mutex.unlock();
341 // Explicit template instantiations
342 template void Thread::split<false>(Position&, Stack*, Value, Value, Value*, Move*, Depth, Move, int, MovePicker*, int);
343 template void Thread::split< true>(Position&, Stack*, Value, Value, Value*, Move*, Depth, Move, int, MovePicker*, int);
346 // wait_for_think_finished() waits for main thread to go to sleep then returns
348 void ThreadPool::wait_for_think_finished() {
350 MainThread* t = main_thread();
352 while (t->thinking) sleepCondition.wait(t->mutex);
357 // start_thinking() wakes up the main thread sleeping in MainThread::idle_loop()
358 // so to start a new search, then returns immediately.
360 void ThreadPool::start_thinking(const Position& pos, const LimitsType& limits,
361 const std::vector<Move>& searchMoves, StateStackPtr& states) {
362 wait_for_think_finished();
364 SearchTime = Time::now(); // As early as possible
366 Signals.stopOnPonderhit = Signals.firstRootMove = false;
367 Signals.stop = Signals.failedLowAtRoot = false;
372 if (states.get()) // If we don't set a new position, preserve current state
374 SetupStates = states; // Ownership transfer here
375 assert(!states.get());
378 for (MoveList<LEGAL> it(pos); *it; ++it)
379 if ( searchMoves.empty()
380 || std::count(searchMoves.begin(), searchMoves.end(), *it))
381 RootMoves.push_back(RootMove(*it));
383 main_thread()->thinking = true;
384 main_thread()->notify_one(); // Starts main thread